The present invention relates to a learning control system for controlling the throttling of an internal combustion engine, the learning control system including a step motor for operating the throttling lever of a fuel supply device which supplies fuel to the internal combustion engine.
There have recently been put to use motor vehicles which incorporate an electronic controller having a microcomputer for controlling an internal combustion engine, a power transmission apparatus, etc.
In such an electronically controlled motor vehicle, the amount of depression of the accelerator pedal operated on by the driver is converted by an accelerator pedal movement sensor into an electric signal which is applied to the electronic control system. The electronic controller then converts the applied electric signal into a step motor drive signal. The step motor drive signal is applied to a step motor which actuates the throttling lever of a fuel supply device that supplies fuel to the internal combustion engine. The throttling control system of such an arrangement includes a fully throttling position switch which coacts with the throttling lever when it is in a fully throttling position. In response to a signal from the fully throttling position switch, the electronic controller detects the fully throttling position of the throttling lever, and then stops applying the step motor drive signal and energizes the coil in the step motor to keep the throttling lever in the fully throttling position. If the fully throttling position switch fails to operate for some reason, then the throttling lever may not be stopped in the fully throttling position, and hence the internal combustion engine may rotate at an extremely high speed, resulting in an undesirable breakdown.
To solve the above problem, there has been proposed a throttling control system for an internal combustion engine, as disclosed in Japanese Patent Application No. 63(1988)-263664. According to the proposed throttling control system, when the fully throttling position switch fails to operate, the opening limit position for the throttling lever, which has so far been the position where the fully throttling position switch is actuated, is set to a preset opening position.
With the proposed throttling control system, therefore, if the fully throttling position switch malfunctions, then the preset opening position is used as a new opening limit position for the throttling lever. Consequently, the internal combustion engine is protected from a possible breakdown and the motor vehicle is allowed to run safely.
Throttling lever actuating mechanisms are generally subject to different manufacturing errors. The steps that step motors have to be incremented to operate the throttling lever in its operating range from the idling position to the fully throttling position may vary from 164 steps to 230 steps. More specifically, the step motor of one throttling lever actuating mechanism may be incremented only 164 steps to move the throttling lever to the fully throttling position in which the engine speed reaches the maximum speed of 4,200 rpm, for example. The step motor of another throttling lever actuating mechanism may be required to be incremented 230 steps before the throttling lever reaches the fully throttling position. Therefore, even if a signal corresponding to 164 steps is supplied to the latter throttling lever actuating mechanism, it cannot move the throttling lever to its maximum position, i.e., the fully throttling position. On the other hand, if a control signal corresponding to 230 steps is supplied to the former throttling lever actuating mechanism, then the throttling lever is forced against the stopper in the opening limit position, causing the step motor to suffer hunting or get out of control and making it impossible to control the throttling lever.
One proposal to cope with the failure of the fully throttling position switch is to include a safety margin when the opening limit position for the throttling lever is changed to the preset opening position. However, since the safety margin necessarily puts the preset opening position below the lower limit of the above range from 164 steps to 230 steps, the maximum output power of the engine cannot be achieved when the preset opening position is selected as the opening limit position for the throttling lever.